40 
had fallen ; but owing to the fact that there was always water 
on the open end I couJdmake no such comparison with the 
barometer as would show that the vacuum in the tube 
Was absolutely free from vapour tension. 
Having obtained from Messrs. Webb of Manchester 
tubes 12 feet long, f inch external and \ inch internal 
diameter, one of these tubes was closed at one end and 
bent so as to leave the closed branch 7 feet 6 inches 
long. The bend is a curve of about 2 inches radius, and the 
two branches or limbs are not quite parallel ; they straddle 
so that at 3 feet 6 inches from the bend they are 7 inches 
apart. At this point the shorter or open limb was again 
bent back through an angle of 160 degrees, so that when 
the main tube is vertical the mouth points downwards. The 
bending of so large and thick a tube was a matter of some 
difficulty, but was successfully accomplished by Mr. Hay- 
wood and Mr. Foster of Owens college. The tube was then 
firmly fastened on to a board by Mr. Foster, and the board 
pivoted on to a stand so that the tube can be turned round 
in a vertical plane. 
The tube being placed so that there was a slight, 
downward incline all the way from the open to the closed 
end, some water was introduced into the open end. 
This having passed down to the closed end and filled 
all the tube, mercury was introduced, which ran down, for- 
cing out the water. As soon as the long limb and the bend 
were full of mercury, the tube was turned into an upright 
position, the mercury sinking down and forcing out the 
water in the shorter limb. Having reduced the water until 
it only occupied about 9 inches above the mercury, the tube 
was again brought into a somewhat horizontal position, but 
this time it was turned so that the mouth was downwards, 
the incline being from the closed to the open end. Before 
reaching that position the pressure of the air had caused 
the mercury to fill the longer limb, leaving only water in 
